1. Field of the Invention
The present invention relates to a heat-flux gage, a manufacturing method thereof and a manufacturing device thereof, and particularly, to a heat-flux gage which is improved from a circular foil heat-flux gage disposed in ASTM (American Society for Testing and Material) E511, a manufacturing method and a manufacturing device thereof.
2. Description of the Background Art
When a temperature difference is generated between metals of difference kinds which are contacted to each other, an electromotive force (emf) is generated due to thermoelectric potential difference between the metals. And heat-flux gage means a sensor for calculating heat-flux amount by multiplying the electromotive force (emf) generated according to above principle by compensating value of heat-flux after mounting the above assembly of two kinds of metals on a heat source which will be measured.
FIG. 1 is a cross sectional view showing a construction and a principle of the heat-flux gage disposed on ASTM E511-73.
As shown therein, a general heat-flux gage has a structure that a circular foil 1 formed by a thermocouple constantan is coupled to a cylindrical body 2 formed by an oxygen-free high-conductivity copper (OFHC).
The heat-flux gage is to generate electromotive force (emf) of mV unit, which is a linear function of the heat-flux, and uses above material because nonlinear movement is shown in case that other metal compound is used.
Two thermocouple junctions are formed on the circular foil 1, one is a heat emission portion coupled to the cylindrical body 2, and the other is a junction with a lead wire 3 connected to a center part thereof.
The lead wire 3 is installed in order to transport a signal from the heat-flux gage to a readout device, and the lead wire 3 is fabricated by twisting a thin leading wire of copper material. The lead wire 3 is generally coated by TFE-fluorocarbon, and protected by a braid overwrap covered by the TFE-fluorocarbon. The lead wire is divided into anode and cathode by colors, and generally, black color is used for the cathode side.
The operation of the heat-flux gage is sensitively affected by surface status, and therefore, a coating by a thin layer of metallic or non-metallic material is generally formed on the surface of the heat-flux gage.
In case that radiant energy is measured, a high-emissive coating is used. It is ideal that the above coating has a diffuse absorbing surface. The diffuse coating is a coating not to change absorption rate by changing incident angle when radiating is generated on the coating.
Also, the ideal coating should have no change in the absorption rate according to the changes of wavelengths, and it is defined as “gray body”. Some coatings approach to the ideal status, however, most coatings have differences from the ideal status.
A metallic coating having low emissivity formed by highly polished gold and nickel is used in a certain case which requires reflection of radiant heat, since the above coating reduces the sensitivity of the gage. The gold coating causes a phenomenon that the output of the heat-flux gage becomes non-linear shape due to rapid change on the thermal conductivity of the gold according to the temperature change.
Hereinafter, principles of measuring heat-flux by the heat-flux gage will be described as follows.
In case that the heat-flux gage is exposed to the heat source, the heat-flux absorbed by the circular foil 1 moves toward the cylindrical body 2 in radial direction, and difference of equilibrium temperature between the center portion of the circular foil 1 and the cylindrical body 2 is generated rapidly. An equilibrium thermoelectric potential (E) between the center portion of the circular foil 1 and the cylindrical body 2 is changed in proportion to heat-flux (q) absorbed into the foil as following equation.Q=KE
Herein, K is a proportional factor set by an experimental result.
Therefore, in case that an appropriate K value is set through the experiment, emf generated on the circular foil 1 and the cylindrical body 2 respectively can be measured by the foil lead wire 3 and a body lead wire 4 to obtain the thermoelectric potential (E) value, and the heat-flux can be measured by above equation.
In order to measure precisely, the temperature should be in a range of 50˜450° F. (−45˜235° C.). In case that the temperature is out of above range, compensation by the change of physical property of the constantan foil is not made, and therefore, the gage does not show the linear movement due to the thermoelectric output any more.
In addition, an idea for fabricating the heat-flux gage has been required since the heat-flux gage should be fabricated very finely in order to obtain precise measured value using the heat-flux gage of above structure.
Especially, the junction of the circular foil 1 and the cylindrical body 2 makes the heat sink, and therefore, another material such as adhesive can not be added thereto. Therefore, the above components should be coupled in a force fit assembly. Thus, an idea for fabrication method of the heat-flux gage by which the above assembling process can be performed simply and finely has been desperately required.
Also, the foil lead wire 3 connected electrically to the circular foil 1 is in a structure that the lead wire is coupled on a plane, and therefore, coupling force therebetween is weak. Thus, a user should be careful when he/she uses the heat-flux gage.